The overall scientific objective is to improve understanding of the macromolecules and filopodia which mediate the interactions between constituents of blood and foreign surfaces under the conditions of cardiovascular use. The proposed studies proceed from preliminary observations with the centrifugal platelet adhesion test. In citrated plasma, platelet adherence to silicone-coated glass is drastically reduced when the shear plane is displaced by a diffused monolayer of uncharged linear polymer if the distance exceeds the length of the fibrinogen molecule. We plan a series of experiments to distinguish the respective roles in platelet adhesion of bridging macromolecules and filopodia. Adhesion will be studied on selected substrates with and without induced platelet shape change and with normal and modified plasma anticoagulated several ways. The observations will be extended to native whole blood flowing over selected substrates present in the form of special bead columns. A variety of tests of blood reactivity will be performed sequentially. When adhesion is minimal the effluent will also be examined for ability to maintain vascular integrity in an ex vivo kidney perfusion assay.